1. Field of the Invention
The present invention relates to a vehicle seat and a method of production thereof.
2. Description of the Related Art
Vital cushion characteristics of a vehicle seat are a proper degree of flexibility, strength enough to carry a load, and durability.
In order to insure such cushion characteristics, conventional vehicle seats have been made up of: a seat frame formed of steel pipe and the like; a spring member such as a urethane pad and a S-shaped spring, which is mounted to the seat frame; and, a covering material such as tricot, moquette, and woven fabrics, which surrounds the surface of the seat frame and the spring member.
However, the spring member formed of the urethane pad, the S-shaped spring and the like requires a large amount of urethane foam, which makes savings in manufacturing costs of the vehicle seat difficult to achieve.
As shown in FIG. 11, a vehicle seat 100 has been proposed for solving this problem (Japanese Utility Model Application Laid-Open No. 61-172560). In the vehicle seat 100, a seat frame 102 is provided with elastic fibers 104 which are spanned in the form of cross stripes. Urethane foam 106 is then integrally overlaid on both upper and lower surfaces of the elastic fibers 104. The elastic fibers 104 acting as a spring layer and the urethane foam 106 acting as a cushion layer are integrally formed into the vehicle seat 100. Therefore, a proper degree of flexibility is thereby expected. In addition, the vehicle seat with a simplified structure and the use of the urethane foam 106 in a reduced amount can be attained.
However, in the above vehicle seat 100, the elastic fibers 104 are spanned in a flat plane with respect to the surface of the seat frame 102. Accordingly, a non-linear deflection curve is drawn in which the amount of deflection in the elastic fibers 104 relative to a load is greatest immediately when the elastic fibers 104 receives a load, and thereafter reduces gradually. (See a solid line in FIG. 9.)
As a result, with this vehicle seat 100, a so-called feeling of sitting-on-the-bottom occurs (by which is meant a feeling of being seated in the bottom of the seat due to unsteady variations of deflections).